1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of driving the same.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, many efforts and studies are being made to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
FIG. 1 is a perspective view illustrating an LCD device according to the related art.
Referring to FIG. 1, the LCD device includes an array substrate 10, a color filter substrate 20 and a liquid crystal layer 30. The array substrate 10 includes a gate line 14 and a data line 16 on a first substrate 12 that cross each other to define a pixel region P. A pixel electrode 18 and a thin film transistor Tr, as a switching element, are positioned in each pixel region P. The thin film transistors Tr, which are disposed adjacent to where the gate lines 14 and the data lines 16 cross, are disposed in a matrix form on the first substrate 12. The color filter substrate 20 includes a color filter layer 26 including red (R), green (G) and blue (B) color filter patterns 26a, 26b and 26c in respective pixel regions P on a second substrate 22, a black matrix 25 between the color filter patterns 26a to 26c, and a common electrode 28 on the color filter layer 26 and the black matrix 25.
Although not shown in the drawings, a sealant is formed along peripheral portions of the array substrate 10 and the color filter substrate 20 to attach the array substrate 10 and the color filter substrate 20 and prevents liquid crystal molecules of the liquid crystal layer 30 from leaking. Further, a lower alignment layer and an upper alignment layer are formed on inner surfaces on the array substrate 10 and the color filter substrate 20, respectively. Further, polarizing films may be formed on outer surfaces of the array substrate 10 and the color filter substrate 20. Further, a backlight supplying light is located below the array substrate 10.
Recently, the LCD device is equipped into electronic devices such as a personal digital assistant (PDA), laptop computer and mobile station. The electronic devices are much used in public places. Generally, users with the electronic devices need information displayed on the electronic devices not to be seen by others. According to the users' needs, an LCD device having two viewing angles, which are different, is proposed. This type LCD device may be referred to as a viewing angle image control (VIC) mode LCD device.
FIG. 2 is a plan view illustrating a VIC mode LCD device according to the related art, and FIG. 3 is a cross-sectional view taken along a line III-III. In FIG. 2, one image display unit includes four pixel regions P1 to P4 which are arranged adjacently into vertical and horizontal directions.
Referring to FIGS. 2 and 3, the LCD device 30 includes an array substrate, a color filter substrate facing the array substrate, and a liquid crystal layer 90 between the array substrate and the color filter substrate.
In the array substrate, gate and data lines 32 and 40 cross each other on a first substrate 31 to define the pixel regions P1 to P4. A thin film transistor Tr is located near the crossing portion of the gate and data lines 32 and 40, and connected to the gate and data lines 32 and 40. A common line 36 is spaced apart from and in parallel with the gate line 32.
The thin film transistor Tr includes a gate electrode 34, a semiconductor layer 39, and source and drain electrodes 42 and 43. A gate insulating layer 36 is on the gate electrode 34.
A plurality of first pixel electrodes 52 each having a bar shape are formed in each of the first to third pixel regions P1 to P3 and connected to the drain electrode 43 of the thin film transistor T through a drain contact hole 48 in a passivation layer 46. A plurality of first common electrodes 38 each having a bar shape are formed in each of the first to third pixel regions P1 to P3 and connected to the common line 36. The first pixel and common electrodes 52 and 38 are alternately arranged. In the fourth pixel region P4, a second pixel electrode 53 having a plate shape is formed and connected to the drain electrode 44 of the thin film transistor Tr.
In the color filter substrate, a color filter layer 76 and a black matrix 73 are formed on a second substrate 70. The color filter layer 76 includes a red (R) color filter pattern, a green (G) color filter pattern, and blue (B) color filter pattern 76c in the first to third pixel regions P1 to P3, respectively. In the fourth pixel region P4, separate color filter pattern is not deposited, and instead, a transparent overcoat layer 79 functions as a white (W) color filter pattern. The overcoat layer 79 is formed over the entire surface of the color filter substrate. A second common electrode 82 made of a transparent conductive material is formed in the fourth pixel region P4. The second common electrode 82 has a plate shape.
In the above-described LCD device 30, each of the first to third pixel regions P1 to P3 is operated according to an in-plane electric field induced between the first pixel and common electrodes 52 and 38. Accordingly, a wide viewing angle of the LCD device 31 can be obtained.
The fourth pixel region P4 is operated according to a vertical electric field induced between the second pixel and common electrodes 53 and 82. This causes a viewing angle of the LCD device 30 to be narrow. In other words, the fourth pixel region P4 is used to control the viewing angle of the LCD device 30 thus the viewing angle can become narrow.
In a case that the LCD device 30 displays texts usually seen in black and white, because of the operation of the fourth pixel region P4, the viewing angle of the LCD device 31 can be effectively controlled such that people around the LCD device 30 does not recognize information displayed on the LCD device 31.
However, in a case that the LCD device 31 displays images usually seen in various colors, since the fourth pixel region P4 does not have separate color filter pattern thus merely displays grays such as black and white, the viewing angle of the LCD device 30 cannot be effectively controlled.
Further, since the fourth pixel region P4 is used for a narrow viewing angle mode of the LCD device 30, when the LCD device 30 is required to be operated in a wide viewing angle mode, the fourth pixel region P4 is not operated thus displays black. Accordingly, brightness of the LCD device 30 is reduced.